Lightweight,plastic,pneumatic feed leg



July 15, 1969 s. F. Juno LIGHTWEIGHT, PLASTIC,' PNEUMATIC FEED LEG Filed June 16. 196'?l INVENTOR J Y L" A'T' States 3,455,212 LIGHTWEIGHT, PLASTIC, PNEUMATIC FEED LEG Sebastian F. Judd, Whitesboro, N.Y., assignor to Chicago Pneumatic Tool Company, New York, N.Y., a corporation of New Jersey Filed June 16, 1967, Ser. No. 646,547 Int. Cl. F15b 7l/08, 15/20; E21c 11/00 U.S. Cl. 91-467 7 Claims ABSTRACT F THE DISCLOSURE Background of the invention Pneumatically extensible and retractable feed legs for rock drills are known in the art having metal piston cylinders and piston rods. These have various deficiencies in that the cylinder and rod are subject to damage, such as denting when struck or dropped, or permanent distortion when unduly overloaded. Damage of this kind is often expensive in that it may require replacement of the damaged members. A feed leg of plastic construction is known from British specification 925,358; however, it has various shortcomings, such as the need of metal inserts, and in the arrangement of its components which differ from that of the present invention, as will later be described.

The general object of the present invention is to provide an improved feed leg of plastic and lightweight construction which avoids the faults of known prior art feed legs and provides, because of its particular construction, various desirable advantages representing a decided advance in the art of feed legs.

Brief summary of the invention In accordance with the invention, there is provided a pneumatic feed leg comprising a piston cylinder formed of plastic material having a closure head at its top end detachably connectible to a rock drill, a piston reciprocable in the piston cylinder having a piston rod formed of plastic material, a bushing fitted in the bottom end of the piston cylinder through which the piston rod slidably extends to the outside of the cylinder, a pronged ground engaging foot mounted to the extending end of the piston rod, the closure head having an externally projecting portion, and a hand operable live air control valve fitted in the projecting portion of the closure head controlling flow of live air to the piston cylinder.

Brief description of the drawings In the accompanying drawings:

FIG. 1 shows in elevation with some parts in section a feed leg embodying the invention;

FIG. 2 is a fragmentary detail showing the control valve in its reverse position; and

FIG. 3 is a pictorial view illustrating the feed leg in association with a rock drill.

Description of preferred embodiment of invention ln the drawing is shown an improved air powered feed leg embodying the invention. The feed leg is designed for use with a conventional pneumatic rock drill, such tent as that shown in broken line at 11 in FIG. 3. The feed leg serves not only to support, but also to feed the rock drill progressively toward the work, such as the face of a rock wall 12.

The feed leg includes an elongated outer piston cylinder 13 relative to which a piston rod 14 is extensible upon application of live air to one end of a piston 15 and is retractable upon application of live air to the opposite end. The cylinder is detachably connectible to a conventional live air feed swivel joint 16 at the underside of the rock drill by means of a coupling comprising a swivel connecting nut 17 and a pipe nipple 18. The piston rod is provided at its bottom end with a pronged foot 19 designed to grip the ground 21 so as to prevent slippage of the feed leg under the load of the rock drill.

Nipple 18 is threaded at its lower end into an externally projecting portion of a closure head 22 mounted to the top end of the cylinder 13. A depending skirt portion 2-3 of the closure head fitted into an open top end of the cylinder has an annular shoulder 24 overlying the end wall of the cylinder. A sleeve nut clamp 25 having an inturned flange 26 overlying the shoulder 24 is threadedly drawn tight upon the cylinder as at 27 to rigidly secure the closure head to the cylinder. A lock screw 28 secures the tightened condition of the clamp. A bushing 29 fitted into the opposite end of the cylinder has an annular shoulder 31 underlying the bottom end of the cylinder. A piston rod wiping sleeve 32 disposed below the bushing has a flange 33 underlying shoulder 31. A sleeve nut clamp 34 having an inturned flange 35 underlying the flange of the wiping sleeve is threadedly drawn tight upon the cylinder as at 36 to fix the position of the wiping sleeve and bushing elements.

The piston rod 14 is of tubular form and of reduced diameter so that an annular chamber 37 is defined between it and the surrounding cylinder. At its upper end, the piston rod is threadedly engaged upon an axially depending stem 3S of piston 15. The piston rod is supported at the bottom end of the cylinder by means of the bushing 29 through which it extends slidably to the outside. rThe external open end of the piston rod is sealed over by means of a cap portion 39 of the pronged foot 19. The cap is drawn tightly into threaded engagement with the piston rod, as at 41.

The piston 15 is slidable relative to the cylinder and to a slender cylindrical tube 42 depending axially of the cylinder. The tube is unitary with a cap plate 43 which is bolted to a recessed wall of the closure head 22. Tube 42 depends axially through the piston into the piston rod for substantially the entire length of the latter, as appears in the retracted condition of the piston rod in FIG. l. An .annular disc 44 fixed to the bottom end of the tube has a loose sliding fit relative to the piston rod.

The application to the zfeed leg of live air supplied through the swivel joint 16 to the pipe nipple 18 is controlled by means of a four-way rotary valve 45 operated by ya hand lever 46. The valve is arranged in the externalportion of the closure head 22. In one position of lever `46, the valve serves to dierct live lair from the pipe nipple 18 to the upper end of the piston and to vent the area below the piston so as to cau-se extension of the piston rod; and in a reverse position of the lever as in FIG. 2, the valve serves to direct live air from the pipe nipple to the bottom end of the piston and to vent the area. yabove the piston so as to cause retraction `of the piston rod.

The piston rod is shown in FIG. 1 in it-s fully retracted condition. To effect extension of the piston rod, the valve is manually turned by means of its lever to the position shown in FIG. l. Live air then flows from the pipe nipple 18 and through the valve 45 to a passage 47 leading to a chamber 48 above the piston causing extension of the piston rod relative to the cylinder. This action serves to pressurize the pronged foot 19 against the ground surface 21 and to pressurize the cylinder against the rock drill whereby the latter is fed toward the work during its drilling operation. As the piston moves downwardly relative to the cylinder, air trapped in the chamber 37 below the piston is forced to escape through ports 49 to the interior of the piston rod from where it passes through ports 51 into the slender tube 42. From tube 42 the escaping air ilows through a passage 52 (FIG. l) in the closure head and is vented through the valve.

To effect retraction of the piston rod, lever 46 is manually turned to reverse the condition of the valve, as appears in FIG. 2. Live air from the pipe nipple 18 now flows through the valve to passage 52 leading into the slender tube 42. From the tube it flows through ports 51 to the interior of the piston rod and out of ports 49 to chamber 37 below the piston causing retraction of the piston rod and release of the forwardly acting pressure of the cylinder upon the rock drill. In this reversed condition of the valve, air trapped in chamber 48 above the piston escapes through passage 47 now leading through the valve to vent.

Supply air to the swivel joint 16 of the rock drill is controlled by conventional means such as a main supply valve on the rock drill 11 and connecting passages (not shown).

The feed leg may be detached from the rock drill by simply uncoupling the swivel nut 17. A handle or hand grip 53 is clamped about the mid-area of the cylinder by means of band clamps S4 is provided `for manual portage of the feed leg.

The particular construction of the feed leg and the particular arrangement of its components provide a multiple of desirable advantages not present in conventional feed legs.

The feed leg is lof lightweight construction. Its metal components are few in number and are formed of lightweight metal, such as aluminum. The cylinder 13, together with its sleeve nut clamps 25, 34 and the tubular piston rod 14, are all formed of plastic material. This overall lightweight construction permits the feed leg to be manually maneuvered about or ported with relatively little physical effort.

Feed legs are subjected to rough use, falling rocks, and overloading so that the metal cylinder and piston rod of conventional feed legs are likely to become damaged as by denting or distortion. Such damage often interferes with piston movement as to require replacement of the feed leg. On the other hand, the plastic structure of the cylinder and piston rod of the present invention are not subject to becoming dented from falling objects or to being permanently distorted and bent. The plastic material of which these components are made has toughness or strength and resilience, as well as some degree of flexibility. When bent under too great Ia load, the cylinder or piston rod readily reforms as its loaded condition is relaxed. When dropped, the cylinder and feed leg merely rebound from the impact without damage. When struck by falling rocks, its resilience causes the rocks to harmlessly bounce olf.

Another problem associated with feed legs is to keep falling debris and dust from entering the cylinder along the piston rod. In the present invention, the cylinder 13 is larranged uppermost, so that the piston rod 14 projecting from the bottom end of the cylinder is protectively guarded. Most of the falling dirt ywill drop harmlessly upon the cylinder.

The plastic construction of the cylinder and of the piston rod is especially suited to the arrangement shown wherein the cylinder is anchored to the rock drill and the piston rod slides relative to the bottom end of the cylinder. Heavy thrusts transmitted by the rock drill to the feed leg are substantially absorbed by the wider cylinder so that there is less tendency of thenarrower piston rod to flex under such loads than would otherwise be the case were the piston rod arranged uppermost. During drilling operations, the greatest load and thrusts are transmitted to the cylinder during the initial part of a drilling operation iwhile the feed leg is in a substantially retracted condition. After the drill has penetrated into the work, much of the load and thrusts of the drill are absorbed by the wall 12 of the drill bore. Accordingly, during the early stages of a drilling operation the feed leg will be relatively retracted and the thrust loads transmitted to the feed leg will be absorbed by the cylinder. During the advanced stages of a drilling operation, the thrust loads of the rock drill will be fairly distributed to the wall of the drill bore and to -both the cylinder and piston rod.

A further advantage of the constructional features of the present invention is the support provided to the cyllinder. This support serves to strengthen the resilient cylinder against flexing under heavy load. In this respect, the elongated metal skirt 23 of closure head and the bushing 29 serve to provide internal backing to the end areas of the cylinder. The piston 15 in its varying positions provides internal backing support to the intermediate areas of the cylinder; and the broad tight band clamps 54 supporting opposite ends of the handle 53 to the cylinder provide a substantial degree of external surface support to the intermediate area of the cylinder.

The plastic material of which the cylinder, the sleeve nut clamps and piston rod are formed has further desirable characteristics. Its surfaces are very smooth. It has self-lubricating characteristics in that it has an inherently greasy and slippery quality which provides desirable bearing surfaces between the cylinder 13 and the metal piston 15, and between the piston rod 14 and the metal bushing 29. This bearing relation permits easy sliding movement of the elements relative to one another without sticking.

Fibre glass reinforced epoxy tubing having its bearing surfaces impregnated or coated with molybdenum disulfide dispersed in an epoxy matrix provides desirable results when used in the construction of the cylinder, sleeve nut clamps, and piston rod. Plastic tubing having the characteristics mentioned herein is known by the trademark Molycor.

Because of the slippery, easy sliding relation of the piston and piston rod relative to the cylinder, there is a tendency during portage of the feed leg for the piston and piston rod to slide extensibly relative to the cylinder. This tendency is Curbed by means of an axial cylindrical pilot extension 55 bolted to the top end of the piston 1S having by means of an O-ring S6 a squeeze t in the skirt 23 of the closure head 22 in a fully retracted condition of the piston rod.

It is understood that air iiow to the feed leg could be regulated by means of a suitable hand control valve arranged in known manner upon the rock drill. In that event, valve 45 would be eliminated from the feed leg structure. It is also understood that the components of the feed leg could be arranged in reverse well-known manner so that the piston rod 14 is extensible from the upper end of the piston cylinder for coupling to the rock drill, and so that the piston cylinder is lowermost and connected with the pronged foot 19. However, neither of these variations would have the full advantages of the structure described and illustrated in FIGS. 1 to 3.

What is claimed is:

1. A pneumatic feed leg comprising a piston cylinder formed of plastic material having a closure head at its top end detachably connectible to a rock drill, a piston reciprocable in the piston cylinder having a piston rod formed of plastic material, a bushing fitted in the bottom end of the piston cylinder through which the piston rod slidably extends to the outside of the cylinder, a pronged ground engaging foot mounted to the extending end of the piston rod, the closure head having an externally projecting portion, and a control valve fitted in the projecting portion of the closure head controlling ow of live air to the piston cylinder, wherein the cylinder is open in its top end, the closure head has an annular flange overlyingr the top end of the cylinder, and a sleeve nut clamp of plastic material having an annular shoulder overlying the said flange has a threaded engagement with the cylinder clamping the closure head rigidly to the cylinder.

2. A pneumatic feed leg as in claim 1, wherein the cylinder is open in its bottom end, the bushing has an annular flange underlying the bottom end of the cylinder, and sleeve nut clamp means of plastic material having threaded engagement with the cylinder clamps the bushing regidly to the cylinder.

3. A pneumatic feed leg as in claim 2, wherein the pronged foot has threaded engagement with the piston rod.

4. A pneumatic feed leg as in claim 3, wherein the piston has an elongated stem depending axially into the piston cylinder, the piston rod is tubular and has a threaded engagement with the stem.

5. A pneumatic feed leg as in claim 4, wherein the cylinder is resilient and is exible under heavy load, and internal and external supporting means is provided to strengthen the cylinder against such exing.

6. A pneumatic feed leg as in claim 5, wherein a hand grip for portage of the feed leg is provided, the hand grip having a pair of band clamps at opposite ends clamped tightly about the cylinder intermediately of the ends of the cylinder in support of the cylinder against flexing.

7. A pneumatic feed leg comprising a piston cylinder formed of plastic material having a closure head at its top end detachably connectible to a rock drill, a piston reciprocable in the piston cylinder having a piston rod formed of plastic material, a bushing fitted in the bottom end of the piston cylinder through which the piston rod slidably extends to the outside of the cylinder, a pronged ground engaging foot mounted to the extending end of the piston rod, the closure head having an externally projecting portion, and a control valve fitted in the projecting portion of the closure head controlling flow of live air to the piston cylinder, wherein the bearing surface of the cylinder relative to the piston is slippery so that the piston rod when clear of the ground during portage of the feed leg has a tendency to slide outwardly relative to the cylinder, the closure head has a skirt depending into the piston cylinder, and the piston has a pilot extension receivable in the skirt with a squeeze fit in a retracted condition of the piston whereby said squeeze fit the tendency of the piston rod to slide outwardly is Curbed.

References Cited UNITED STATES PATENTS 866,720 9/1907 Gilman 173-36 2,068,660 1/1937 Curtis 173-36 XR 3,040,712 6/1962 Harrah 92-170 XR 3,044,413 7/1962 Corsette 92-170 XR 3,059,586 10/1962 Brailsford 92-170 3,085,638 4/1963 Larcen 91-467 XR 3,110,530 11/1963 Herman 308--238 3,345,021 10/1967 Granston 173-36 XR CHARLES J. MYH RE, Primary Examiner HARRY B. RAMEY', Assistant Examiner 

